This invention relates generally to an electrical switch and particularly to an opposed contact switch in which a movable contact is brought into contact with stationary contacts.
An opposed contact type switch is advantageous in that the movable contact is moved into and out of engagement with the stationary contacts with less frictional resistance and the points of the contacts are scarcely worn. However, it is disadvantageous in that the contacts are liable to degrade in electrical conduction because oxide films are formed on the contact points. In order to overcome the difficulty, heretofore the contacts have been made of gold-based material or silver-based material. Accordingly, the conventional opposed contact type switch suffers from the drawback that the material cost is high and the manufacturing cost is, as a result, also high.
In addition to the opposed contact type switch, a sliding contact type switch has been alternatively employed. The sliding contact type switch is advantageous in that the contacts can be made of relatively inexpensive copper-based material because the oxide films are removed by the sliding of the movable contact. However, it is still disadvantageous for the following reason. As the movable contact is moved between the stationary contact from the start of contact until the movable contact reaches the final contact position, the force of friction between the movable and stationary contacts is very large. In order to reduce the frictional force, lubricant such as grease is applied between the two contacts. However, in this case, the contacts are liable to suffer degradation in insulating properties because a large quantity of metal powder scraped off the contacts by the friction becomes mixed with the lubricant and the lubricant becomes conductive.